1. Field of Invention
This invention pertains generally to the production of nanomaterials and, more particularly to the production of carbon graphenes and other nanomaterials.
2. Related Art
Nanomaterials is an emerging new field to which major efforts in research and development are being applied. The characteristics of nanomaterials can differ significantly from those of conventional materials in a number of respects that may be important to applications in many fields, including the medical field, semiconductors, energy storage, advanced composites, electronics, and catalytics. Many nanomaterials can be used in ways that exploit their quantum-mechanical properties.
Recently, significant research and interest have been focused on graphenes. Graphenes are allotropes of carbon in the form of one atom thick sheets of carbon atoms densely packed in a hexagonal honeycomb crystal lattice. Graphenes have a number of unique and desirable qualities, including extraordinary surface area, electrical conductivity and capacitance, thermal and mass transfer capability, magnetic properties, and extraordinary values of tensile strength and modulus of elasticity. These attributes, individually or in combination, are projected to make carbon graphene structures applicable to a number of important technologies and markets, including electrolytic storage media for lithium ion batteries and ultra capacitors, facilitated transport membranes for micro filtration, catalysis as substrate material, heat transfer for light-emitting diodes (LEDs) and other applications, high frequency semiconductors for computing, hydrogen storage, conductive materials for flatscreen and liquid crystal displays (LCDs), and strengthening agents for advanced materials in wind turbines and automobiles. IBM has demonstrated a 100 gigahertz graphene transistor and stated that a 1 terahertz transistor graphene is conceivable.
There are a number of known methods for producing graphenes, including chemical vapor deposition, epitaxial growth, micro-mechanical exfoliation of graphite, epitaxial growth on an electrically insulating surface, colloidal suspension, graphite oxide reduction, growth from metal-carbon melts, pyrolysis of sodium ethoxide, and from nanotubes. Each of these methods has well documented advantages and disadvantages. A general advantage of many of the processes is the ability to produce relatively pure graphene materials and, in some cases, large continuous surface graphene materials. Processes such as epitaxial growth and colloidal suspension may lead to the customization of graphene materials to suit very specific requirements.
There are also a number of known methods for producing other forms of carbon nanomaterials such as nanospheres, fullerenes, scrolls and nanotubes, including, for example, the use of carbon arc and laser technologies.
To date, however, no process for the production of carbon nanomaterials has been successfully commercialized, despite many serious efforts to do so, particularly with respect to carbon nanotubes. Therefore, there is justified concern that commercial production of graphenes may also be difficult to realize. All the known graphene formation processes have significant limitations and disadvantages, including the dependency on relatively scarce highly crystalline graphite as feedstock, high cost, and limited scalability. Because of these limitations, the known methods may not be capable of providing a dependable supply of low cost graphenes with high volumes of production.
The invention is based upon an extremely robust and scalable reaction in which the preferred reagents or feedstock are carbon dioxide (CO2) and magnesium (Mg).
When carbon-based fuels such as coal, oil, and natural gas are variously combusted to generate heat, substantial amounts of CO2 and other combustion products are produced, and there is widespread concern about the historically high and increasing amounts of CO2 in the atmosphere. Scientists believe the unusually high levels of CO2 in the atmosphere could cause or are already causing adverse global climate effects and acidification of the oceans. While a number of solutions have been proposed for the reduction of CO2 emissions, the dominant model in publications and public policy debate involves capture of the CO2 by one or another of several chemical mechanisms, followed by compression of the captured CO2 and, finally, disposition of the CO2 as a waste product by injection (sequestration) into the earth. Since the capture of CO2 from fossil fuel emissions is costly and energy intensive, it would be desirable if at least some of the captured CO2 be put to productive use rather than be treated as a waste product. An economically feasible, large scale, and profitable process for reduction of CO2 to carbon products would create demand for captured CO2 and reduce the requirement for sequestration of CO2.
There are a number of known methods for the reduction of CO2. One such process is photosynthesis, which is a widely appreciated and prolific CO2 reduction mechanism that reduces CO2 to carbon that is then used by the living system to produce complex organic molecules which are necessary for life. However, photosynthesis has the disadvantage of being difficult to replicate in technical or man-made biologic systems.
Ferrous Oxides, including magnetite and several other similar mineral compounds, have also been found to beneficially reduce CO2 to an amorphous form of carbon. Likewise, liquid potassium has been found to beneficially reduce CO2 to amorphous carbon. In addition, there are a number of partial reduction (mineralization) processes in which CO2 is converted to carbonates. Partial reduction approaches are currently considered more likely than full reduction of CO2 to carbon to be feasible alternatives to sequestration because full reduction of CO2 is generally believed to be steeply endothermic and, therefore, economically challenging. However, partial reduction approaches have the disadvantage of producing materials for which the market prices are relatively low.
In sum, previously known CO2 reduction methods are limited practically and economically by one or more factors, including cumbersome mass flow requirements, significant energy requirements, high cost of reactants, difficult or risky materials management, and/or low value of the end products, with the value of the products often being less than the cost of producing them.
Magnesium is not presently found in nature in pure form and must be produced by one or more well-known methods from one or more of its natural existing forms, which include magnesium chloride and magnesium oxide. Magnesium is frequently produced from seawater where it resides naturally as the second most abundant cation. In this production process, the Mg is precipitated with calcium hydroxide, and the precipitant is reacted with HCl and finally reduced to magnesium by electrolysis. Other processes, including the Pidgeon process, which utilize heat to reduce mined magnesium rich ore, are employed to produce relatively pure magnesium. However, these processes are relatively expensive and do not always produce the level of purity desired.